Note: Descriptions are shown in the official language in which they were submitted.
~ 3039Z9
A PUMP AND A FLUID DISPENSING DEVIC~
INCORPORATING A PUMP
This invention relates to pumps of a small size
particularly though not exclusively implantable pumps
which are sufficiently small for use within the human
body.
Pumps of small dimensions are used in implantable
drug dispensing devices where a medicament is to be
- dispensed to an ambulatory patent on a regular or
intermittent basis over an extended period of time, as
where in~ulin is dispensed in the treatment of a
diabetes, or where chemotherapeutic drugs are dispensed
in the treatment of cancer. In these circumstances it
is advantageous in the treatment with the drug to
perform an automatic dispensation of the drug without
having to rely upon pills or injections. Thus a unit is
implanted within the patient comprising a reservoir of
the drug and a pump, the pump being under control of a
control circuit which may be coupled by an
electromagnetic transmitter and receiver to an external
control source.
Such a device for delivering the drug must be
reliable in operation, sealed against body fluids and
must hold a sufficient quantity of medication so as to
avoid the need for frequent refills and must be
refillable when empty. Furthermore, such dispensing
systems must be physically small so as to be readily
implantable without unnecessary disturbance of the baby.
It is known to employ in such dispenslng devices
pumps such ~s the peristaltic type or solenoid type.
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staltic pumps operate by responding to blood pressure
within the body and solenoid pumps operate under control
of a internal battery connected to a solenoid for
operating a suitable pump mechanism. However such pumps
are relatively large, and considering their size, are
inefficient within the context of implantable units.
The present invention is based on the concept of a
pump which incorporates a mechanism which is actuated by
means of a piezo electric element. Such a pump can be
made of a very small size and is therefore suitable for
use in an implantable drug delivery systemO However
such a pump may be of use in whatever application where
the requirement is for a pump of very small size.
An aspect of this invention is as follows:
A dispensing device, comprising:
a housing forming a reservoir for fluid to be
dispensed and a pump for dispensing the fluid located
within the reservoir;
said pump including a pump chamber, a movable pump
element and a piezoelectric element, said pump element
being physically contiguous with and directly coupled to
said piezoelectric element whereby changes in dimension
of said piezoelectric element induce pumping movement in
the movable pump element;
a source of electrical power connected to a control
means for cyclically applying electrical voltage to said
piezoele¢tric element for inducing periodic changes in
dimension in said piezoelectric element;
a first one-way valve member being directly
connected between the fluid reservoir and the pump
chamber for permitting flow of a fluid from said
reservoir into said pump chamber upon movement of the
pump element and a second one-way valve member
connected between the pump chamber and an outlet for
dispensing said fluid from said pump chamber; and
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means for maintaining the pressure of khe fluid in
the reservoir as the fluid is being dispensed, said
pressure maintaining means including an expandable
member having one end connected to said pump which
closes a space defined by said expandable member.
Thus since all that is required to provide the pump
motive power is a piezo electric element and a source of
electrical power such as for example a battery, and that
furthermore since the piezo electric element is
contiguous with and directly coupled with the movable
pump element, with no intervening shaft or push rod, the
piezo electric pump may be made very small in
dimensions.
The electrical power cupplied to the piezo electric
element from the battery may be in pulsed d.c. form or
alternatively and as preferred for efficiency it may be
AC, with a suitable inverter circuit being provided.
The movable pump member may be of any suitable
type, rotatable or displaceable, and the piezo electric
element
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may be coupled to the pump member in such a way as to
induce the required type of movement. In a preferred
embodiment, the movable pump member comprises a flexible
membrane movement of which increases or decreases the
size of a pump chamber which is coupled to a drug
reservoir and an outlet port by suitable one way valves.
Thus a decrease in volume of the pump chamber causes a
drug within the pump chamber to be expelled through the
valve of the outlet port, the valve at the inlet port
remaining closed, whereas when the volume of the pump
chamber is increased by movement of the membrane, the
one way valve at the outlet port is closed whereas the
one way valve at the inlet port is opened to permit
- further drug to be introduced into the pump chamber. As
preferred the piezo electric element comprises a planar
element extending over a substantial or major part of
the surface area of the membrane and being firmly
affixed to the surface thereof. Thus when dimensional
changes are induced in a suitable direction in the piezo
electrical element, this causes the piezo electric
element to curve in one or two opposite directions from
the plane in which it is disposed and ~he consequent
bowing effect of the element causes a corresponding
deformation of the membrane resulting in similar type of
movement of the membrane. Thus the pump may be
configured as essentially a flat disc-like 1ement, with
the piezo electric element/ the membrane forming the
movable pump member and the pump chamber all being of
essentially planar form.
A preferred embodiment of the invention will not be
described with reference to the accompanying drawings
wherein:
Figure 1 is a view in elevation of the exterior of
an implantable dispenser incorporating a pump according
to the invention'
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Figure 2 is a schematic cross-sectional view o~ the
dispenser of Figure l;
Figure 3 is a view in cross-section of the pump o~
the implantable dispenser; and
Figure 4 is a block diagram of the electrical
control circuit of the implantable dispenser.
Referring now to the drawings there is shown an
implantable dispenser 2 for use in a drug delivery
system where the dispenser is implanted into the body o~
a human being and is operative to dispense into the body
suitable quantities of a drug at intervals under control
of a circuit within the dispenser and as required under
external control by means of a receiver/transmitter
arrangement. The dispenser 2 as shown in Figure 1
comprises an outer casing 3 of bio-compatible material,
for example titanium alloy or stainless steel or
biologically compatible silicon rubber. The dispenser
body comprises a main portion 4 which is circular in
elevation with a diameter of 3.5 cm (this dimension and
the dimensions quoted below arP approximate). The depth
of the main portion 4 is 2.5 cm. A lobe portion 6 is
provided having a width as measured from the
circumference of the circular portion 4 o~ 1.5 cm and
having a dspth of 1.5 cm.
The overall configuration of the implantable
dispenser is shown in Figures 2 and 3 as comprising a
septum 8 mounted in lobe portion 6 and containing a
radially compressed block o~ silicone rub~er, an inlet 9
being provided for external access and a passageway lo
to a main drug reservoir region 12. In use, the
reservoir 12 is ~illed by insertion of the hypodermic
needle of a syringe into the silicone rubber insert via
a passageway 9, so that the drug flows into the main
reservoir region 12 via a passageway 10. Extra~tion of
the needle when the reservoir is filled automatically
closes the silicone block. Valves 14, 16 are provided,
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130392~
inlet valve 14 permitting entry of the drug into a pump
18 and outlet valve 16 permitting exit of the drug from
the pump body to a delivery catheter 20 which extends
from the dispenser body to a suitable location within
the human body. The pump is connected to an electronic
control circuit by means of electrical leads 24, the
electronic circuit being powered by a b~ttery 26. A gas
spring is provided in the area 30 between the pump and
the electronic circuit 22 within the volume enclosed by
lo a bellows 32. The function of the gas spring ig to
maintain an essentially constant pressure in reservoir
12 as the quantity of drug decreases during infusion.
By selectiny a suitable mixture of "Freon"-type
hydrocarbons which liquify at about one bar pressure,
the pressure in the gas spring can be made to remain
effectively constant (apart from the spring
charactaristics of the bellows) as the drug is used up
and the bellows 32 opens.
The pump is shown in more detail in Figure 3 as
being of generally flat and planar shape being 3.0 cm in
diameter and 2 mm thick. The pump comprises two plate
members 30, 32 of pressure moulded titanium alloy and an
intermediate plate 34 is also formed of titanium alloy.
These plates define a port 36 for inlet valve 14 housing
a freely movable valve member 38 and communicating with
a passageway 40. Passageway 40 form~d in intermediate
plate 34 communicatas with a pump chamber 42 and a
further channel 44 formed in plate member 34
communicates with an outlet valve having a freely
movable valve member 46 which is mounted in a recess 4
which communicates with ou~let 50.
Titanium plate 32 defines a movable member to which
is bonded a circular plane piezo electric sheet 52.
Suitable seals are provided (not shown) surrounding the
valve members, the seals and valve members being made o~
biologically compatible materials, for example silicone
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rubber. The three plates 30, 32, 34 are sealed together
by a technique such as electron beam welding or
diffusion bonding. The piezo electric element 52 is
mounted on plate 32 using a conductive epoxy fillsd with
silver.
In operation, when an electric voltage is applied
across the thickness of the piezo electric element 52,
this creates a bowing, resulting in the central part of
the piezo electric element moving out of the plane of
the element a certain amount whereby to cau~e a
corresponding deformation in plate 32 and thus causing
an expansion or contraction of volume of the pump
cham~er. Where expansion is caused, this creates a
- suction effect causing valve member 38 to be moved
downwardly allowing drug from reservoir 12 to flow into
the valve chamber. Outlet valve member 46 is
maintained against passage 44 during this movement.
upon contraction of the space of the pump chamber caused
by inward movement of plate 32, valve member 46 is
pushed upward by permitting a drug to flow through tAe
outlet valve 16.
Referring now to Figure 4 there is shown the
electronic circuitry for controlling the pu~p comprising
an inductive loop antenna 60 which receives electrical
signals from external control apparatus. This is
connected to a receiver and transmitter 62, 64 which in
turn provide and receives signals from a central control
logic 66. A lithium battery 26 is coupled via a battery
checking circuit 68 to control logic 66. Electronics
circuits 70 are provided coupled to sensors which are
situated within the pump to monitor conditivns such as
battery charge, critical operating voltages, internal
humidity, pump/valve monitoring, quantity of drug in
reservoir and rate of dispensation, clock settings and
stored operating system. In addition sensors may be
situated at parts of ths human body to determine from
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biological conditions whether a drug should be
administered. The control logic is al90 coupled to an
oscillatory driver 72 which includes an inverter circui-t
and which provides alternating current to the pump for
causing a pumping action of the pump. It may thus be
seen that the pump can be controllPd in any suitable
manner to provide a reyular or intermittent flow or drug
to a person having this dispenser device implant-
therewithin, the pump being controlled either internally
by sensor devices mounted within the patient or
externally by means of signals transmitted
electromagnetically from an external control device.
The pump as described delivers very small
quantities of fluid, as shown about 0.1 micro litres per
pump sample. The advantages of the pump as described
are its very small size and its cheapness as compared
with peristaltic pumps or solenoid pumps and the pump is
therefore very suitable for applications where accurate
guantities of liquid must be pumped in small amounts and
where a pump of small size is required.
